For the pst 2 weeks or so I've had a weird misfire issue in my XJR. Idles fine but under medium to heavy acceleration... the car hesitates for about a second or so like it's misfiring while trying to accelerate. I don't think it's the ignition coils anymore since I've switched out 3 sets already and I still have this issue.

I did try to put in a different ECU which I think is when this problem started but I've since then switched it back to my original ECU. Could the other ECU messed with my TPS(throttle position sensor) or CSPS(crankshaft position sensor)?

Cruising on the highway is fine and idling at a redlight is fine also. Only happens most of the time when I'm merging onto the freeway and attempting to overtake.

 

Sounds like a transition problem in the fuel trim. Have you given the MAF a good cleaning? From your description, it sounds like it is occurring as you go from closed loop to open loop mapping. You might try a "hard boot".

Your other ECU might have different calibration and orientation, but this ecu should be just like it was when you exchanged them.

Pray tell, why did yiou change the ECUs in the first place?

 

Same issue here, AlbBolivar,


I believe my problem to be with a 'low spot' on the TPS. Hard to get one used at a decent price in Canada, and out of the question new, so the search continues lol.

 

I think that's exactly it. When I look at my scan gauge while accelerating the misfiring starts as soon as it goes to open loop.
What would be the causes of that and how would I fix it?

 

What I THINK that would imply is that the open loop control parameters are not being read correctly as the fuel map is being determined. So, either the measured air is wrong, the temperature is measured wrong or, just as likely, what Shaune said, the measured position of the throttle is wrong. I suppose the fuel pressure could be wrong, there could be a vacuum leak, or there could just be a reason that the ignition system is marginal and will not fire as the mixture changes.

What do the STFT and LTFT look like just before and after the transition?

I assume you have followed the great plug debates. If in doubt, the plugs for this engine are pretty cheap and easy to change.

 

i had major idling/stalling issues with my XJR, 6 months ago
diagnosis was complicated by the modified ECU not talking to the PDU
So in the end, new TPS, temp sensor, AFM solved it. Plus new gaskets on intake side (there were some leaks)
While it was apart, a new Eaton was put on for good measure.

it runs fine now, but still idles a bit high at times (1000 rpm); rest of time rock steady at about 700 rpm

could your problem be a coil failing under load?

 

The only things I can think of I did recently where this issue started to happen was changing out the ECU (reason I did that was because when my IACV is plugged in with my original ECU, the idle is very high and leaving it unplugged fixes that issue), changing out the coils, switched them from another x300 (but I think that was just a coincidence that it started happening because I changed out the coils and ECU at the same exact time), I also replaced my thermostat (I did notice my old one opened up at around 176F and this new one I got doesn't open up until 194F.

Could the thermostat make a difference like that?
The misfire issue does still happen before the car is fully warmed up, at about 150F I accelerate at about 2500-3200RPMS and it sometimes misfires/hesitates....

As far as the STFT and LTFT goes... it's been "this and that" sometimes.
For example the other night, I was on my way home and I decided to unplug the MAF but the misfires were still happening so I just decided to plug it back in. While cruising down the freeway, I noticed that my STFT were all the way to -25.0 and it stayed there for maybe a good 15 miles or so.

And as for the plugs... I switched them out to brand new NGK coppers I would say about 10 months ago and this issue just started happening.
I've lightly followed the "plug debate" but never really found an issue with these plugs. Been running them in my XJ6 for the past 3 years or so and not one issue with them. So I highly doubt it has anything to do with the plugs... at least I hope not. Unless the oil sneaking into the plug wells would do that, but then again that's been leaking since I got the car, just haven't gotten around to removing the cam cover.

 

well, I would have a good look at the TPS readings while slowly moving the throttle. The TPS calibration of the "bad" ecu would cause the symptoms you report.

 

Quick little update. Drove out to Arizona over the weekend which was about a 600 mile trip with the XJR.

On the way out there, I noticed that the misfires only happened when it went into open loop. So cruising down the freeway wasn't a big deal. Which was making me think that it would be the TPMS not reading the correct throttle position.
I have my other ECU in the trunk so when I got to Arizona, I decided to switch them out and see how it performed... funny thing is it does pretty much the exact opposite of my "original" ecu. Hard acceleration, the car pulls fine. It's when I'm coming to a stop, the car starts to misfire and about every minute or so when I'm on the freeway, the car will slightly hesitate, I'm sure someone not looking for a problem won't notice it but it's there.

Now I'm wondering if somehow my original ecu "forgot the default fuel maps"? and the ecu I switched out just needs to be setup correctly through WDS/IDS?
After switching out the ecu, I think I can rule out the TPMS being faulty?
I haven't had a chance to take the car with the replacement ecu to get it setup but I'm hoping that'll fix my issues.

 

The ecu must have the correct orientation for the O2s- which sensor is connected to which connector and the correct TPS calibration. Without that, you will get strange behavior- which you have. Open loop fueling uses the MAF, the temperature, and the TPS.

 

Ah, didn't think about that when I was reading through this thread, good catch.

When one changes the TPS (and I think O2 sensors), the ECU must be oriented by the dealer (or equiv software), so conversely if one switches out an ECU that ECU likely isn't properly oriented either.

Can't say why the original ECU is acting up though, although fitting a new TPS was mentioned earlier.

.

 

During my drive out to Arizona, I was thinking that it was the TPS (I just realized I kept saying 'TPMS') since it would happen when I opened up the throttle but now with the replacement ECU, shouldn't I be getting the same issues?

I wonder what messed up the mapping with my original ECU though...

 

I guess you either do not understand or you do not believe that each TPS is calibrated to each ECU, by settings in the ECU. So, it should be no surprise that one ECU would behave differently from another ECU unless they were each calibrated to the same TPS.

 

DUH. I just realized what you guys have been trying to tell me. I was always thinking that there was an issue with the TPS itself and wasn't realizing that the ECU controlled that also. I guess I was thinking you were telling me the TPS was malfunctioning

 

So, see if you can find someone with IDS or WDS software who will do a "TPS calibration" and a "Lmbda Orientation" on each module for a reasonable price. Take a cross country trip to GA and I will let use my software for free!.

 

I have. I've actually been planning on taking it to a shop for the past 2 weeks but haven't had the chance.

One place I called told me they would only do it if it was a brand new ECU but I'm not sure if it is because I picked it up from a buddy who had it traded to him for other parts. Another place says they can do it for $90, I think that's reasonable.

Do you know why the first place wouldn't do it unless it's a brand new ECU? Also how long does that process usually take?


I wish I could take you up on that offer. I don't know people here with dealer level software, if I did, I'd be messing with my software even more haha

 

No, I cannot imagine why. The ECU in an X300 is not field programmable (you only change parameters) and requires a PROM change to change the program. It takes more time to get the IDS running than to do the setups, but most shops charge a 1 hour minimum, so $90 sounds right. They will do both modules for that, right?

 

I'm not exactly sure. I just called and simply explained to them that I changed ECU's in the car and I need them to do a "new engine setup" and if they had the computer to do that. Their reply was simply "yes and it's $90".
Are you talking about both ECU modules or the PROM inside the ecu itself?

 

No, they cannot change the Prom programs. I refer to orienting and calibrating both modules to the car.

 

Oh. That I'm not sure. I had only planned on doing one module but now I'll ask them to do both